1. Field of the Invention
This invention relates to spark plugs for use in internal combustion engines.
2. Prior Art
U.S. Pat. No. 3,202,859 issued to Knaggs teaches a spark plug in which a central electrode extends above the end of the spark plug. The elongated central electrode is surrounded by an insulator which is, in turn, surrounded by the ground electrode. The ground electrode is an annular shell which is in direct contact with the insulator. There is no air gap in this construction and the spark generated travels along the surface of the insulator from the central electrode to the ground electrode.
U.S. Pat. No. 4,087,719 issued to Pratt, Jr. teaches a spark plug with an insulator between an annular ground electrode and a central live electrode. The central electrode has a sparking surface which is not covered by the insulator. The annular ground electrode is attached to the spark plug body. The annular electrode and the central insulator are not in direct contact with any air gap.
U.S. Pat. No. 3,683,232 issued to Baur teaches a spark plug cap wherein a capacitance is connected between a live electrode lead and ground. The extra capacitance functions to increase the intensity of the spark generated at an air gap between the live electrode and the ground electrode.
Further improved ignition is desired in engines using a lean air to fuel ratio. In particular, it would be desirable to produce in high swirl engines a stable discharge with both greatly increased arc length and ionization volume without significantly higher required breakdown voltage, thus leading to improved ignitability. These are some of the problems this invention overcomes.